Although having a generally similar "look" or overall appearance, a careful study of natural wood grain patterns or moire ("watered") silk patterns reveals that such patterns are essentially unique non-repetitive random patterns. Considerable effort has been directed to duplicating wood grains and other naturally varying patterns. For example, table tops which are created by laminated plastics (or other suitable processes) often include a sheet on which a pseudo wood grain has been printed.
The nature of such presently practiced processes is that the patterns produced, while attempting to appear to be natural, random patterns, are in fact repetitive. For example, "wood grain" patterns produced by conventional printing processes such as the roller press, rotogravure, letter press, etc., include large patterns formed by repeating smaller patterns. Thus, rather than being truly random, patterns produced by such devices are formed of readily discernible repetitive pattern lengths.
In addition, the printing devices which have heretofore generated such patterns have significant limitations. For example, rotogravure printing, when used for printing "wood grain" patterns on linoleum and other floor coverings, requires laborious preparation of extremely large diameter printing rolls. The printing press structure to support these rolls is massive. Moreover, to change the printing pattern in a rotogravure process requires that an entire new roll be engraved and inserted into the printing press.
The present invention provides apparatus for applying to a wide range of substrates random patterns, such as wood grains, that accurately simulate unique and non-repetitive patterns observed in nature. In addition, the present invention provides a highly flexible process for generating a wide range of such patterns.
As will be explained in detail below, the apparatus of the present invention may be readily controlled to change the spacing and the nature of random patterns being produced. Additionally, with the present invention, random patterns may be superimposed on other patterns, e.g., letters symbols, pictures, photographs, to create a wide range of aesthetically pleasing effects.
The patterns produced by the present invention may be broadly denoted as "random interference" patterns. Such patterns may include wood grain, moire (watered silk, waterfall or other related patterns.
Interference patterns, which are generically referred to as "moire" patterns in a Scientific American article by Oster et al typically result from the superposition and resulting interference between two periodic sub-patterns (e.g., two angularly oriented gratings). Such interacting sub-patterns must have transparent regions if they are to be superimposed as in Oster et al, Scientific American, May, 1963 pages 54-63.
The "moire" silk pattern shown on page 54 of the Oster et al article results from the superposition of two sets of nearly parallel cords to produce a fabric having a shimmering appearance resembling the wavelike reflections on the surface of a pool of water. The interference pattern phenomena is such that a tiny displacement between two nearly aligned arrays of lines will be greatly magnified.
In the present invention, an electrostatic jet applicator is uniquely controlled to selectively create random interference patterns which simulate wood grain, "moire" silk and other related patterns. Initially the operation of the fluid jet applicator will be generally described followed by a detailed disclosure as to how the random interference patterns are generated.
The electrostatic fluid jet applicator of the present invention is designed to apply a fluid (e.g., a liquid dye) to a moving substrate (e.g., paneled wall ceiling material, fabric, etc.) by: (a) selectively charging and recovering some of the fluid droplets continuously ejected from a stationary linear array of orifices affixed transverse to movement of the substrate, while (b) allowing remaining selectively uncharged droplets to strike the substrate (e.g., thereby forming an image on the substrate).
More particularly, fluid is supplied to a linear array of liquid jet orifices in a single orifice array plate disposed to emit parallel liquid streams. These liquid jets break into corresponding parallel lines of droplets falling downwardly toward the surface of a substrate moving transverse to the linear orifice array. A droplet charging electrode is disposed so as to create an electrostatic charging zone in the area where droplets are formed (i.e., from the jet streams passing from the orifice plate). A downstream catching means generates an electrostatic deflection field which deflects all charged droplets into a catcher where they are typically collected, reprocessed and recycled to a fluid supply tank. In this arrangement, only those droplets which happen not to get charged are permitted to continue falling onto the surface of the substrate.
In prior art fluid jet applicators, great care is typically taken to produce droplets that are regularly and precisely spaced, sized, and timed across the orifice array in order to permit proper use of the apparatus. It is well recognized that such uniform droplet production is adversely affected by non-uniform stimulation across the orifice array due to reflected and interfering waves (i.e., so as to produce "standing" waves) such that certain orifices do not have the appropriate stimulation while others have too much.
In accordance with conventional wisdom, prior art fluid jet applicators have been designed to eliminate or reduce such standing wave patterns in order to achieve proper applicator operation. In such applicators, the orifice plates have been limited in length, employed dampening control and many other techniques to eliminate the problems caused by standing wave patterns.
The fluid jet applicator of the present invention utilizes a piezoelectric crystal to artificially stimulate the fluid supply chamber with coherent acoustic energy to purposely generate and exploit the acoustic standing waves therein. As a result, although substantially uniformly sized droplets will be formed at substantially the same frequency from each orifice, individual droplets will be formed so as to be out of phase with adjacent neighbors in accordance with the standing acoustic wave pattern. By selecting only a very short print time, e.g., such that only one or two drops are formed within such a print time and by controlling the frequency of such print time, a wide range of aesthetically appealing, unique, random interference patterns can be created and printed. Patterns closely simulating natural wood grains (including knot holes) can be readily produced by the present invention. Moreover, the present invention allows patterns to be modified with relative ease and remarkable flexibility.